Sleep apnea is a sleep disorder characterized by pauses in breathing during sleep. By definition, sleep apnea is the cessation of airflow to the lungs during sleep which lasts for at least 10 seconds, and is usually associated with more than a 4% drop in blood oxygen saturation (“SaO2”) level. There are three distinct forms of sleep apnea: central; obstructive; and complex. Complex sleep apnea is defined as a combination of central and obstructive sleep apnea. It is estimated that central, obstructive, and complex sleep apnea account for approximately 0.4%, 84% and 15% of the reported cases, respectively. With central sleep apnea, a patient's breathing is interrupted by the lack of respiratory effort. With obstructive sleep apnea, partial or complete collapse of airways interrupts patient breathing. With complex sleep apnea, there is a transition by a patient from central sleep apnea characteristics to obstructive sleep apnea characteristics during breathing.
Obstructive sleep apnea (“OSA”) is the most common respiratory disorder that may lead to a myriad of problems including daytime fatigue, irritability, impaired concentration, poor job performance, increased risk of accidents, and cardiovascular problems. OSA is most common in people with high blood pressure, people with a narrowed airway due to tonsils or adenoids, and people who smoke tobacco products. OSA occurs more frequently in elderly, and is more common among males than females.
Currently, polysomnography (“PSG”) is a preferred tool for diagnosing sleep apnea. PSG includes a comprehensive recording of biophysiological changes in a patient during sleep. A typical PSG test includes recording various biological signals, including brain signals (“EEG”), heart rhythm signals (“ECG”), muscle activity or skeletal muscle activation signals (“EMG”) of chin and legs, nasal airflow signals, electro-oculogram or eye movement signals (“EOG”), and abdominal and thoracic movement signals. A disadvantage of PSG time gathering and evaluating the biological signals is time consuming. Further, PSG is inconvenient and expensive because it requires a full night of patient supervision by a healthcare professional.
Alternative technologies for diagnosing sleep apnea may record a reduced number of signals and detect apnea events during sleep. Many of the current technologies record patient airflow. In these technologies, patient breathing airflow may be measured by either a face mask or a nasal cannula connected to a pressure transducer, and cessation of patient breathing airflow is detected as the main diagnostic sign of sleep apnea, particularly OSA. In the case of mouth breathing by a patient, which may occur often during the night, the nasal cannula will not register airflow. Therefore, a nasal cannula is not very reliable. On the other hand, using a face mask, which is considered a more reliable device for breathing airflow measurement, may change the breathing pattern of the patient. Additionally, it is difficult for some patients to fall asleep wearing a face mask.
A majority of people (˜70%) who undergo a full-night sleep study are not diagnosed as severely apneic. Therefore, there is a need for a non-invasive system and methods to pre-screen patients suspected of sleep apnea that avoids the inconveniences of current invasive respiratory airflow detection devices such as nasal cannulae and masks. The present invention satisfies this demand.